Thanks guys. So it sounds like for a quick/dirty workflow - Iridient Developer followed by Affinity to edit the developed Tiff might be the way to go. Both are Mac centric which works for me. For large projects where the Sessions or even Catalog interface is beneficial then C1 might be the answer.
One of the issues I have with C1 is they tend to be slow in updating their code for OSX updates although Apple releases preliminary releases of the new OS in plenty of time. For example Iridient already supports the new Apple processor as does Affinity. Adobe is following suite. So does Microsoft Office and heavy lifting mathematics S/W Mathematica. Matlab is release that update in December.
But C1 - they won't say and they were late to the party on the last update.
IMO Affinity is a very good Photoshop replacement but it's not first and foremost a raw developer. I use it alongside C1.
Yes C1 are always a bit coy with news about new versions, but David Grover from C1 dropped a very big hint this week that there is likely to be a major announcement from C1 before the next scheduled Quick Live online editing session on 26 November - I assume that will be regarding their C1 21 version, which will "officially" also be compatible with Big Sur.
However, I gather from the Mac Talk board that the current version of C1 is working OK with Big Sur, with some members reporting that it's working
"definitely faster" .
In general though, other than neophile urges, I don't why people are so keen to upgrade their OS as soon as possible - personally if your current OS version is working fine, what's the big rush? In fact, I think there are good arguments to wait a little while.